TLDR

Fixes #3536.

Apply TransportOptions.setEnv(...) to the Java SDK ProcessBuilder before starting the Qwen Code CLI subprocess. The adapter already merges System.getenv() with the caller-provided env map, but the merged map was never wired into the child process.

Screenshots / Video Demo

Terminal evidence:

Before this change, the focused regression failed because the child process printed an empty value:

expected: <from-set-env> but was: <>

After this change:

mvn -Dtest=ProcessTransportTest#shouldPassCustomEnvToProcess test
# BUILD SUCCESS; Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

Dive Deeper

TransportOptionsAdapter#addDefaultTransportOptions() already builds the intended subprocess environment by starting from System.getenv() and overlaying TransportOptions.getEnv().

ProcessTransport#start() now copies that handled env map into processBuilder.environment() before start(), so Java SDK callers can pass values such as proxy, sandbox, model, or other runtime configuration variables to the CLI process as documented.

Reviewer Test Plan

1. From packages/sdk-java/qwencode, run mvn -Dtest=ProcessTransportTest#shouldPassCustomEnvToProcess test.
2. Confirm the new test creates a temporary executable, passes QWEN_SDK_TEST_ENV through TransportOptions.setEnv(...), and reads the value from the child process output.
3. Inspect ProcessTransport#start() and confirm the handled env map is applied before processBuilder.start().

Testing Matrix

Java SDK validation run on macOS:

mvn -Dtest=ProcessTransportTest#shouldPassCustomEnvToProcess test
mvn -DskipTests test
mvn checkstyle:check
git diff --check

All passed. I did not run npm run preflight; this patch is limited to the Maven-based Java SDK package, and the existing package test file includes live-CLI tests that can depend on local auth/provider state.

Linked issues / bugs

Fixes #3536